1. Field of the Invention
The present invention relates to a wire-cut, electric discharge machining method, and more particularly to a wire-cut, electric discharge machining method which automatically measures the offset value required by using the wire electrode to measure the size of a wire electrode spark gap, and which machines the workpiece while correcting the machining path in accordance with the measured offset value.
2. Description of the Prior Art
Wire-cut, electric discharge machining methods machine a workpiece by producing a discharge between a wire electrode and the workpiece. In using such methods, it is necessary that the center of the wire electrode be disposed at a position offset from the desired profile of the workpiece by a distance corresponding to the sum of one half of the wire diameter plus the size of the spark gap. The spark gap varies in size depending upon the voltage and current necessary for machining the material and the thickness of the workpiece. The desired offset value also differs for each machining operation and undergoes a further change during the actual machining operation. To compensate for these changes in offset value, it is the general practice of the prior art to predetermine the offset value of each portion of the workpiece by performing test machining prior to main machining, but this practice is very troublesome.
For example, as shown in FIG. 1, when cutting a circular arc shape by wire-cut, electric discharge machining, the radius of curvature of an actually machined shape 10 becomes smaller than that of the intended configuration 11. Such an error may be caused by a delay in the machining path due to sagging of the wire electrode under the pressure of discharge in the dielectric fluid, or by a difference in the quantity of machining between the two side walls of the workpiece because of their different radii of curvature; but the precise cause has not yet been determined. In order to avoid such a configuration error, the prior art adopts a method of pre-correcting the machining path when the NC tape is prepared. However, this method is defective in that much time is required for the correction and, when the workpiece or machining condition is changed, the correction must also be altered.